This invention relates to a connector plug used for interconnection of audio-equipments, video-equipments, personal computers and their peripheral equipments.
A connector plug has been proposed in Japanese Utility Model Publication No. 59-79986, entitled "Connector Plug," which has two features. One of the features is that although the plug is small in size, it can provide a strong force, with which it is held fitted in a connector socket, and offer a strong resistance against a force tending to pull it out of the socket so that it is less liable to be accidentally detached from the socket. The other feature is that although it is small in size, it permits ready positioning of pins when it is inserted into the connector socket.
The structure of this prior art connector plug will now be described with reference to FIGS. 1 to 6. FIG. 1 shows a perspective view of the connector plug. It comprises a cylindrical metal cover 101, which accommodates an insulating body 102 fitted into it. A plurality of contact pins 103 extend through insulating body 102 in the axial direction of cylindrical metal cover 101. This example of the connector plug has five contact pins 103. Metal cover 101 is covered by an insulating cap 104 except for its front portion. Insulating cap 104 has a rear cable protector portion 105, through which a cable 300 is led out from metal cover 101.
This prior art connector plug structure has two features. One of the features is that metal cover 101 is cylindrical. The other feature is that a front portion of metal cover 101 has a main positioning ridge 106 and a plurality of auxiliary positioning ridges 107a and 107b, these ridges protruding radially inwardly from the inner cylindrical surface of metal cover 101. Main positioning ridge 106 is distinguished from auxiliary positioning ridges 107a and 107b by its shape and size. Main positioning ridge has a greater circumferential width dimension and a greater height than auxiliary positioning ridges 107a and 107b. Due to this difference in shape, main positioning ridge 106 is prevented from being engaged in a recess or groove on the socket side, in which auxiliary positioning ridge 107a and 107b is to be engaged. The plug thus can be inserted in a fixed orientation.
The front ends of main and auxiliary positioning ridges 106, 107a and 107b are offset a fixed distance L from the front end of cylindrical metal cover 101. Cylindrical metal cover 101 has a cut-away part 108 open at its front end. Cut-away part 108 is provided for avoiding engagement of the plug with a portion of the socket and permits size reduction of the socket.
Insulating body 102 has an insulating bar-like member 109 integrally extending forwardly from the front end thereof together with contact pins 103. Insulating bar-like member 109 is provided at different positions according to the number of contact pins 103 provided in insulating body 102. FIGS. 2 to 4 show connector plugs having different numbers of pins 103. Insulating bar-like member 109 is provided at different positions in the front end of these connector plugs. The connector plug shown in FIG. 2 has three pins. The connector plug shown in FIG. 3 has four pins. The connector plug shown in FIG. 4 has eight pins. In these examples, eight pins are the maximum number of pins that are carried together. With the connector plug having the maximum number of pins, insulating bar-like member 109 is omitted. That is, insulating bar-like member 109 is provided on only the connector plugs having three to seven pins.
The mating socket is provided with a hole, in which insulating bar-like member 109 is to be received. The positional relation between insulating bar-like member 109 and the socket hole prevents erroneous insertion of a plug into a socket for a plug having a different number of pins. Insulating bar-like member 109 has a slightly greater length than contact pins 103, by which it extends from insulating body 102, than contact pins 103. Thus, it is only when insulating bar-like member 109 is first inserted into the corresponding hole in the socket that contact pins 103 can then be inserted into corresponding contact pin holes in the socket.
FIG. 5 shows the internal structure of the prior art connector plug. Contact pins 103 are preliminarily planted, for instance by forced piercing, in insulating body 102 such that their contact portions project from the front end of insulating body 102 and their connecting terminal portions project from the rear end of insulating body 102. Insulating body 102 with contact pins 103 is inserted into cylindrical metal cover 101 from the rear end thereof. Wires of cable 300 are preliminarily soldered to the connecting terminal portions of corresponding contact pins 103 projecting from the rear end of insulating body 102.
Cylindrical metal cover 101 is formed by pressing a resilient metal sheet into a cylindrical form. The opposite edges of the metal sheet are free edges to permit resilient deformation of the cover in the diametrical direction. Cylindrical metal cover 101 has a plurality of protuberances 301 projecting from the inner peripheral surface thereof. These protuberances 301 are adapted to be received in recesses 302 formed in the outer periphery of insulating body 102 when insulating body 102 is inserted into cylindrical metal cover 101.
When insulating body 102 is inserted until protuberances 301 are engaged in recesses 302 of insulating body 102, inwardly bent portions 303 of cylindrical metal cover 101 formed rearwardly of protuberances 301 are engaged in recesses 304 formed in insulating body 102 at the circumferential edge adjacent to the rear end. Insulating body 102 thus is locked in cylindrical metal cover 101 by protuberances 301 and bent portions 303.
Cylindrical metal cover 101 has a cable clamp 305 extending from its rear end. Cable clamp 305 consists of an arcuate clamp portion 306 and a connecting portion 307 connecting clamp portion 306 and the rear end of cylindrical metal cover 101. Clamp portion 306 has a plurality of inner teeth 308.
After insulating body 102 has been installed in cylindrical metal cover 101, clamp portion 306 of cable clamp 305 is bent inwardly to wedge it into the insulating cover of cable 300. Cable 300 is secured to cylindrical metal cover 101 with the wedging of teeth 308 of clamp portion 305 into the insulating sheath of cable 300.
After cable 300 has been secured by cable clamp 305 to cylindrical metal cover 101, the cylindrical metal cover with insulating body 102 is set in a mold for resin molding to form insulating cap 104 integrated with cable protector portion 105, as shown in FIG. 6. During the resin molding of insulating cap 104 and cable protector portion 105, the resin intrudes into the interior of cylindrical metal cover 101 through openings 309 or windows that are formed when forming inwardly bent portions 303, whereby cylindrical metal cover 101 and cable 300 are molded into insulating cap 104 and cable protector portion 105.
This prior art connector plug has the following advantages.
(a) Since metal cover 101 is formed by bending a metal sheet into a cylindrical form (unlike a still earlier prior art connector plug where a cylindrical metal cover was assembled from two semi-cylindrical halves), the resiliency of the cylindrical metal cover in the diametrical direction can be increased. It is thus possible to provide a connector plug which can be held fitted in a mating connector socket, and which offsets a strong resistance against a force tending to pull it out from the socket.
(b) Since the connector plug has main positioning ridge 106 and two or more auxiliary positioning ridges 107a and 107b, when the end portion of cylindrical metal cover 101 is inserted into an annular groove of the mating connector socket, these ridges 106, 107a and 107b are engaged with the cylindrical wall defining the annular groove, whereby the plug is supported. Therefore, for finding the inserting position of the plug, the plug can be turned without being inclined, i.e., with its axis coincident with the axis of the connector socket. Thus, the operation of finding the plug insertion position can be facilitated.
(c) The provision of insulating bar-like member 109 assures that the plug cannot be inserted into the socket unless the contact pins of the plug corresponds in number to the pin insertion holes of the socket. Therefore, there is no possibility of erroneous insertion of a plug into a socket which is provided for a plug having a different number of pins. Erroneous electric connection thus can be prevented. Further, the engagement of insulating bar-like member 109 in the corresponding hole in the socket helps to support the plug in the socket without rattling.
With the plug having eight contact pins, the eighth contact pin 103h (as shown in FIG. 4) is provided at a position different from the position of insulating bar-like member 109 of a connector plug having a different number of pins. Therefore, even without insulating bar-like member 109, the plug will never be erroneously inserted into a connector socket for a plug having a different number of pins, particularly the plug having seven pins.
(d) Since insulating bar-like member 109 extends a slightly greater distance from the insulating body than contact pins 103, contact pins 103 will never be inserted into contact pin holes of the socket unless insulating bar-like member 109 is first inserted into its corresponding hole in the socket. Thus, a two-fold positioning can be obtained, i.e., one positioning function is provided by positioning ridges 106, 107a and 107b and the other positioning function is provided by insulating bar-like member 109. This has an effect of preventing the erroneous contact of a contact pin of a plug with a contact of an irrelevant circuit on the socket side when an attempt is made to find the proper inserting position of the plug.
(e) In the internal structure, arcuate clamp portion 306, which constitutes a portion of cable clamp 305 and has inner teeth 308, is bent to close the corresponding end of cylindrical metal cover 101, thereby causing teeth 308 to wedge into the insulating sheath of cable 300. The length of the plug thus can be reduced compared to prior art plugs having different cable clamp structures.
With this connector plug, however, insulating body 102, to which cable 300 is connected, is inserted comparatively deeply into cylindrical metal cover 101. This operation is rather cumbersome. In addition, the plug is manufactured by connecting cable 300 to contact pins 103 extending from insulating body 102, then inserting insulating body 102 into cylindrical metal cover 101, then inserting the plug portion of cable 300, i.e., cylindrical metal cover 101 with insulating body 102 fitted therein, into a mold for resin molding to form insulating cap 104 with cable protector portion 105. Therefore, the manufacture is rather complicated. The operation of inserting cylindrical metal cover 101 with cable 300 connected thereto into the mold and setting it in a predetermined position in the mold is particularly cumbersome and requires considerable man-hour.
Further, since insulating cap 104 is molded to cover cylindrical metal cover 101, no repair can be done when cable 300 and a contact pin 103 become disconnected from each other.
Further, insulating cap 104, as shown in FIGS. 1 to 6, consists of a comparatively thin cover wall covering the outer periphery of cylindrical metal cover 101. Therefore, when a portion of insulating cap 104 near the front end is gripped, the gripping fingers are very liable to touch cylindrical metal cover 101 because of the small thickness of the wall of insulating cap 104. When cylindrical metal cover 101 is touched by a finger, any electric charge carried by the user's body is discharged to cylindrical metal cover 101. The discharge voltage is coupled through cable 300 to an input or output terminal connected thereto of an electronic apparatus. In such a case, rupture of a semiconductor element or the like connected to the terminal is liable to occur.
Further, while cable clamp 305 may permit size reduction of the plug, its mechanical strength is low because cylindrical metal cover 101 is made from a thin sheet material. Therefore, with this prior art connector plug it is necessary to reinforce cable clamp 305 by inserting a rear portion of cylindrical metal cover 101 inclusive of cable clamp 305 into a resin constituting insulating cap 104.
Further, in case of the still earlier connector plug which was provided prior to the prior art connector plug shown in FIGS. 1 to 6, the cylindrical metal cover was assembled from two semi-cylindrical halves as mentioned before. This connector plug, therefore, had the problems of loose mounting of the metal cover and inaccurate relative positioning between the two semi-cylindrical halves. To solve these problems, it has been necessary to increase the axial dimension or length of the insulating body. In addition, the metal cover should have a large wall thickness and a high mechanical strength. Further, it has been necessary to use an insulating cap having a large wall thickness in order to secure the assembly consisting of the insulating body and metal cover to the insulating cap. Therefore, the size of the whole plug has been inevitably large.